Air heater



Dec. 16, 1930. J 5, BLACK 1,785,334

AIR HEATER Filed March 4, 1926 W W, I l/VVENTOR BY I I v "ATTORNEYS Patented Dec. 16, 1930 UNITED STATES PATENT OFFICE JOHN E. BLACK, OF RUMSON, NEW JERSEY, ASSIGNOR TO THE BABCOCKda WIICOX COM- PANY, .OF BAYONNE, NEW JERSEY, A CORPORATION OF NEW JERSEY AIR HEATER This invention relates to an air heater that v is especially useful in connection with steam boilers, and will be understood from the description and theaccompanying "drawing g which shows a vertical section through the means of the nipples 4. Hot products of combustion from the furnace F of the boiler,

pass .across the tubes 1, and then between the nipples 4, and down along the feed water preheater or economizer 5, as shown by the arrows, and enterthe lower ends of the heating elements or tubes 7 of the air heater, and pass out through the smoke stack 8. The tubes 7 are connected to header plates 9 and 10 and are enclosed in a housing that may be rectangular in cross-section, the side walls of which are shown at 11 and 12, with the tubes 7 distributed all the way across between the other two walls.

Baflies 13, 14 and 15 as long as the distance between the other two -walls, extend across the tubes 7. A plate 16, which is likewise as long as the distance between the two walls, is located between the tubes 7 and wall 12 and is as wide as the distance between bafiies 13 and 15. Dampers or closure members 17 are hinged at the ends of the plate 16, and are of such dimensions as to close the spaces between the plate 16 and the wall 12 when they are in the closing positions. Similar dampers 17 are hinged at the ends of'the plate 16 and close the spaces between plate 16 and baffles'13 and 15 when they are closed. A damper 18 is hinged near the middle of plate 16, and is of suflicient dimensions to close the space between this plate and the edge of the baffle 14. A damper or baflie member 19 is hinged-at the wall 11, and is of sufficient dimensions to close the space between the baffle 14 and the wall 11.

The air pump or fan 20 forces air through the duct 21 across the heating elements or tubes 7 of the air heater, through the duct 23 into the suction fan or pump 22, from whence the air .passes through the duct 24 to the furnace of the boiler, where it is used for combustion purposes, the hot products passingacross the boiler tubes 1, as above mentioned.

The operation is as follows: When the boiler is operating at normal load, the dampers 17 and 17 are turned to close the spaces between the plate 16 and the wall 12 and between the plate 16 and the tubes 7, and the damper 18 is also turned to leave the space between the battle 14 and the plate 16 open, and the damper 19 is turned to close thespace between the wall 11 and baffle 14. The air passes, as shown by the arrows, through the duct 21 across the upper ends of the tubes 7 thence in a reverse direction across the tubes between the baffles 13 and 14, thence again across the tubes between the baflies 14 and 15, and finally across the tubes below the baffle 15 into the duct 23 and fan 22, through the duct 24 to the furnace. When the boiler is being forced, a part of the air may be bypassed around the heater by opening the dampers 17, so thataportion of the air does not come into contact with the air heater tubes 7. The dampers 18 and 19 may be adjusted, so that only a portion or none of the air that passes across the upper ends of the tubes 7, passes across the portions between the bafiles '13 and 15. The dampers 17, 18

and 19, may be adjusted to different positions to vary the proportions of air that is to be by-passed entirely around the tubes or around a portion of the same, as above described.

In other words it will be seen that the duct and the preheater are arranged in parallel so that the air may follow parallel paths through either the duct or the preheater. The

word parallel is not here used in a geometrical sense but in the same sense as in describing electrical circuits; that is, there are two paths between the fans 20 and 22 which the air from the fan 20 may take.

With air by-passed around the air heater, it is possible to operate the pressure fan 20 or suction fan 22 at less pressure or suction,

respectively, or a larger volume of air can be delivered by the same fans than would be the case if all the air were passed through all the passes of the air heater, withthe consequent frictional resistance and drop in air v were used.

pressure. Either one of the fans 20 or 22 may be dispensed with, thus operating the device by forcing air through the heater by the fan 20 when the fan 22 is not used, or by suction of a r through the air heater by means of the fan 22, when the fan 20 is not used. When a boiler is operated without a feed water heater, the hot exit gases may be at a sufilciently high temperature to heat the air to such a point as to give trouble at the stoker. In such cases, the dampers of the air heater can be operated so as to prevent the air from being heated to too high a temperature.

By making provision for by-passing some of the air at high ratings, the air velocity at normal ratings can be increased, thereby increasing the efiiciency of the air heater surface. If no provision were made for bypassing the air at peak loads, the velocity thereof would be reduced unless extraordinarily large fans and driving means therefor Another advantage of by-passing air at certain loads is that the fans can be designed to run at high average efficiency over wide boiler ratings, as a suflicient amount of air can be by-passed with diflerent boiler ratings to give a somewhat uniform load on the fan.

When it is desired to change the heater from a four-pass to a two-pass heater, the

' dampers 17 are opened, the damper 18 is closed and the damper 19 is opened, thus causing the air to pass over the heating surIace of the air heater twice and increasing the area of flow, thereby reducing materially the resistance of flow of the air through the heater, and at the same time utilizing the total surface of the air heater. A portion of the air may be by-passed by opening the dampers 17, whether the heater is operated as a fourpass or as a two-pass air heater.

I claim:

1. A fluid heater having hollow heating elements, means for passing one fluid through the elements and another fluid in contact with the other surface of the elements a multiplicity of times, and means for varying the number of passes for the latter fluid.

2. In combination, a duct adapted to supply air to a furnace, a preheater arranged in parallel with saidduct, and means to deflect through said preheater either a partor the whole of the air passing through said duct.

3. In combination, a duct adapted to sup ply air to a furnace, a preheater arranged in parallel with said duct and having a plurality of passes through which the air may travel, meansfor deflecting air from said duct through said preheater, and means for varying the number of passes without substantially changing the amount of heating surface to which the air is exposed while passing through the preheater.

4. In combination, an air heater having a plurality of heating elements, means to pass hot gases through said elements, means forming parallel spaces on opposite sides of said elements, a plurality of baflies extending across said elements to form passes communicating with said spaces, and a damper in each of said spaces and each adapted when in one position to cooperate with one of said bafiles to form an extension thereof and when in another position to permit air to flow past the end of the battle.

5. In combination, an air heater having a plurality of heating elements, means to pass hot gases through said elements, means forming parallel spaces on opposite sides of said elements, a plurality of bafiles extending across said elements to form passes communicating with said spaces, a plate in one of said spaces and extending lengthwise of said elements, and a damper pivoted on the side of said plate next the elements and adapted when in one positionto cooperate with one of said bafiles to form an extension thereof and when in another position to permit air to flow past the end of the baflle.

6. In combination, an air heater having a plurality of heating elements, means to pass hot gases through said elements, means forming parallel spaces on opposite sides of said elements, a plurality of baflies extending across said elements to form passes communicating with said spaces, a plate in one of said spaces and extending lengthwise of said elements, a damper pivoted on the side of said plate next the elements and adapted when in one position to cooperate with one of said baflies to form an extension thereof and when in another position to permit air to flow past the end of the bafiie, and a damper on the other side of the plate and adapted to control passage of air through the space on that side of the plate.

7. An air heater comprising heat-ing elements, means for passing a heating medium through said elements, means forming a plurality of air passes across said elements, said passes embracing substantially the entire eating surface of said elements, means for causing the air to flow in opposite directions in adjacent passes, and means for changing the direction of air flow in one of said adjagen;1 passes to cause a parallel flow through 8. An air heater comprising heating elements, means for passing a heating medium through said elements, means for causing air to flow over substantially the entire heating surface of said elements, and means for varying the number of passes taken by the air in its flow over said surface.

9. An air heater comprising heating elements, means for passing a heating medium through said elements. means forming a plurality of air passes across said elements, said passes embracing substantially the entire heating, surface of said elements, means for causing the air to flow in opposite directions I in adjacent passes, and means forcombining ad'acent passes to form a 'larger pass.

10. air heater comprising heating elements, means for passing a heating medium through said elements, means for causing air to flow over substantially the entire heating surface of said elements, means for varying the number of passes taken by the air in its flow over said surface, and means for by-, passing the air around all of said elements.

JOHN E. BLACK. a 

